Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Zedman on June 18, 2016, 07:01:42 am

Title: Suitability of Marshall JCM 900 50w Dual Reverb 4500 for test build
Post by: Zedman on June 18, 2016, 07:01:42 am

Hello Folks, Im hoping some of you can help me out. Im a noob here so I will try and tread carefully.

Im looking to build a 50w Marshall style amp head so that I can learn more about tone mods and circuit design.

Unfortunately I suffer the tyranny of distance as Im in Australia and the cost of transporting heavy/ bulky items is considerable.

Although I realise that a Marshall JCM 900 50w Dual Reverb 4500 suffers a poor reputation which I agree with, I have the opportunity to get one at a decent price. The EL34 forums have some posts about gutting and converting these amps.

So my question is, are the PT and OT in these amps of sufficient quality to make as a good enough base for conversion?

A similar chassis in Aus costs about $300AUS on its own! Even if a rebuild costs a couple of hundred in parts, I may be better off than starting from scratch and importing the lot.

OK any help will be appreciated.
Cheers
Z

Title: Re: Suitability of Marshall 4550 for test build
Post by: sluckey on June 18, 2016, 07:45:00 am

I can't find any info on Marshall 4550. Are you sure about that number?

Title: Re: Suitability of Marshall 4550 for test build
Post by: mresistor on June 18, 2016, 08:40:43 am

The only 4550 I know of is the  David Bray  4550, so I think the OP is talking about a 50 watt plexi.     http://www.davidbrayamps.com/vicjohnson.html (http://www.davidbrayamps.com/vicjohnson.html)


Did you mean Marshall 2550 Jubilee re-issue? 

Title: Re: Suitability of Marshall 4550 for test build
Post by: Zedman on June 18, 2016, 05:09:17 pm

oops my bad that was a finger error.

Its a Marshall JCM 900 50W, model 4500. The Dual Reverb that is part solid state front end

cheers
Z

Title: Re: Suitability of Marshall JCM 900 50w Dual Reverb 4500 for test build
Post by: sluckey on June 18, 2016, 06:02:38 pm

Quote

So my question is, are the PT and OT in these amps of sufficient quality to make as a good enough base for conversion?

yes

Title: Re: Suitability of Marshall JCM 900 50w Dual Reverb 4500 for test build
Post by: Zedman on June 18, 2016, 07:09:33 pm

Thanks Mr sluckey!
Z

Title: Re: Suitability of Marshall JCM 900 50w Dual Reverb 4500 for test build
Post by: tubenit on June 18, 2016, 09:15:24 pm

I gutted one yrs ago and turned it into sort of a Plexi 50w with a paralleled V1 tube.  Sounded great.

with respect, Tubenit

Title: Re: Suitability of Marshall JCM 900 50w Dual Reverb 4500 for test build
Post by: Zedman on June 18, 2016, 11:42:02 pm

Thanks Mr tubenit, it was your posts that gave me the idea that this would be a good place to start.

Starting using an existing amp should save me a good deal of money. I did some research yesterday and everything is expensive here- even the wooden case for a Marshall style head is about $300AUS. Add in the chassis, PT, OT and hardware I can see that it will all add up too quickly.

Thanks for the help fellas, its much appreciated.

Z

Title: Re: Suitability of Marshall JCM 900 50w Dual Reverb 4500 for test build
Post by: uki on June 20, 2016, 12:40:34 pm

Have you thought about making your own chassis and cabinet?

Check out uncle doug's videos on youtube lots of valuable information there:
https://www.youtube.com/user/Stratosaurus1/videos (https://www.youtube.com/user/Stratosaurus1/videos)

Constructing a Finger-Jointed Pine Amplifier Cabinet
https://www.youtube.com/watch?v=GTLfe9UViwE (https://www.youtube.com/watch?v=GTLfe9UViwE)

Also check out on youtube how to bend aluminum plates to make the chassis.

Title: Re: Suitability of Marshall JCM 900 50w Dual Reverb 4500 for test build
Post by: pompeiisneaks on June 20, 2016, 04:04:22 pm

I've tried doing both chassis and cabinet, and have learned that although I'm pretty good at building amps, I'm not good at building chassis' and cabinets :) 

They don't look too bad, but I didn't enjoy making them, and was fully sick of the process when I finished :)

But you should definitely give it a try once, there's a pretty significant sense of accomplishment on completing it.

~Phil

Title: Re: Suitability of Marshall JCM 900 50w Dual Reverb 4500 for test build
Post by: Zedman on June 23, 2016, 04:04:55 am

thanks Fellas, one day I may give this a go but these days I am really considering the value of my time.

If I can earn more money, than purchase cost, by doing repairs in the same time it would take to make something its a no brainer.
Z